Q.

Let f(x)=2x-x2,  xR. If m and n are respectively the number of points at which the curves y=f(x) and y=f'(x) intersect the x-axis, then the value of m+n is _________.                 [2024]


Ans.

(5)

We have, f(x)=2x-x2

By graph, since f(x) intersects the x-axis at 3 points. So, number of solutions of f(x)=3

  m=3

Also, f'(x)=2xlog2-2x

By graph, since f'(x) intersects x-axis at 2 points. So, number of solutions of f'(x)=2

  n=2

Thus, m+n=3+2=5